Blood loss in patients with severe trauma can be significantly worsened by coagulopathy, a condition in which blood fails to clot appropriately. Hemorrhage is the cause of 40% of trauma deaths worldwide. Acidosis, hypothermia, and coagulopathy constitute a “bloody vicious cycle” of massive trauma, hemorrhage, resuscitation, hemodilution, coagulopathy and continued bleeding. The coagulopathy of trauma is a deficiency in the body's mechanism for blood clotting, observed as bleeding from non-injured sites such as intravenous lines and tissue oozing after surgical management of identifiable vascular bleeding. Over the past several years studies have pointed to the coagulopathy of trauma as an early event that is identifiable at the time of presentation, and more importantly, that early coagulopathy predicts higher mortality. This has led to efforts to identify patients at high risk of coagulopathy and to pre-empt it by such strategies as early plasma transfusion, in both military and civilian trauma.
Instruments to study and measure the coagulation and clotting properties of blood include technologies based on measuring shear forces, chemical reactions, and optical transmission. The thromboelastograph (TEG) [U.S. Pat. No. 6,225,126] is a device that measures the shear forces on a pin suspended in a droplet of blood sitting in a cup via a wire. As the cup is rotated back and forth through a small angular displacement the clot formation causes torsion on the wire, which is measured by the instrument. The TEG directly measures the change in viscoelastic behavior as the clot is formed. This instrument is a standard device used in the diagnosis of coagulopathy. The volume of blood used by the TEG is large enough to require sampling from a patient's veins and the instrument is very vibration sensitive. An alternative device performs a chemical measurement to determine the response of a blood sample to the drug warfarin [U.S. Pat. No. 5,526,111]. Another instrument on the market is an optical turbidity monitor that uses a simple photodetector and light source. The photodetector based instrument monitors the transmission of an incoherent light source through a blood sample, and when the transmitted light reaches a predetermined threshold correlated with clot formation the elapsed time is recorded [U.S. Pat. No. 4,777,141]. Another instrument uses the displacement of ferrite beads [U.S. Pat. No. 3,695,842]. The instrument detects magnetic flux through a ferrite bead immersed in a blood droplet. The displacement of the bead during coagulation is measured through changes in the magnetic flux.